Close contacts between chalcogen atoms in cyclic dienes and diynes are used to create columnar structures in the solid state. Rigid and fairly planar cycles with chalcogen centers are the preconditions for forming those columnar structures.

The reaction of 1,4,8,11-tetrathiacyclotetradeca-2,9-diyne (7) with C 5 H 4 (CO 2 Me)Co(CO) 2 (8) and C 5 H 4 (SiMe 3 )Co(CO) 2 (10) led to the tricyclic cyclopentadienone complexes 9 and 11. In both species the CO was inserted into a former triple bond. This observation led to the preparation of the tetrathiaalkyl-and tetrathiaaryl-substituted C 5 H 4 (CO 2 Me)Co-capped cyclobutadiene complexes 23 and 27-30. When these compounds were heated under a pressurized CO atmosphere at 170 °C, the corresponding cyclopentadienone complexes 9, 15, and 31-33 were formed. Model calculations at the B3LYP level of theory on tetrasubstituted (R ) CH 3 , SH, (CH 2 ) 3 , S-CH 2 -S) CpCo-capped cyclobutadiene complexes showed that the substitution, especially by SH and S-CH 2 -S, considerably lowered the energy of the assumed intermediate metallacycles 35 and 36, which opens the possibility of reaction.

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Dicarbonyl(η5‐cyclopentadienyl)cobalt(I) (1) reacts with the electron‐poor alkyne bis(tert‐butylsulfonyl)acetylene to give the corresponding cyclobutadiene complex 6, whereas the reaction of [CpCo(CO)2] with dimethyl acetylenedicarboxylate yields the cyclopentadienone complex 7 under the same conditions. The cyclobutadiene complex 6 could not be obtained by the treatment of [η2‐bis(tert‐butylsulfonyl)acetylene](carbonyl)(η5‐cyclopentadienyl)cobalt(I) [3(H)] with an excess of bis(tert‐butylsulfonyl)acetylene. The same holds for the treatment of 3(H) with dimethyl acetylenedicarboxylate and bis(catecholatoboryl)acetylene. With these results we assume that the monoalkyne complex 3(H) is not an intermediate in the alkyne oligomerisation of electron‐poor alkynes, as was shown for electron‐rich ones. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Keywords: Alkynes / Cobalt / Cyclopentadienyl ligands / N ligandsThe electron-rich aminoacetylenes Et 2 NC 2 R (2a-c, R = SPh, PPh 2 , and Ph, respectively) react smoothly with [η 2 -bis(tertbutylsulfonyl)acetylene](carbonyl)(η 5 -cyclopentadienyl)cobalt (1) to form the donor-acceptor stabilized (η 4 -cyclobutadiene)cobalt complexes 3a-c in good yields. However, treatment of the electron-poor borylacetylenes 2d-f with the cobalt complex 1 does not lead to the expected (η 4 -cyclobutadiene)cobalt complexes. Analogously, the reaction of bis(1-